2-Chloropropanoic acid, CH3CHCICOOH, is used in many chemical syntheses.

1. (a)(i)An equilibrium is set up when CH3CHCICOOH is added to water. Write the equation for this equilibrium.[1]
2. (a)(ii)0.150 mol of CH3CHCICOOH dissolves in 250 cm³ of distilled water to produce a solution of pH 1.51. Calculate the pKa of CH3CHCICOOH.[2]
3. (a)(iii)An equal concentration of aqueous propanoic acid has pH 2.55. Explain the difference in the pH of solutions of equal concentration of CH3CHCICOOH and propanoic acid.[2]
4. (b)(i)Alanine is an amino acid. Its isoelectric point is 6.1. State what is meant by isoelectric point.[1]
5. (b)(ii)Give the structural formula of alanine at pH 2.[1]
6. (b)(iii)Alanine exists as a pair of optical isomers. The structure of one optical isomer is shown in Fig. 5.2. [Figure 5.2] Draw the three-dimensional structure of the other optical isomer of alanine.[1]
7. (b)(iv)Polymer C forms from the reaction between alanine and 4-aminobutanoic acid, H2N(CH2)3COOH. Draw a repeat unit of C. The functional group formed should be displayed.[2]
8. (b)(v)State the type of polymerisation shown in (b)(iv).[1]
9. (b)(vi)Scientists are investigating C as a replacement for poly(propene) in packaging. Suggest an advantage of using C instead of poly(propene).[1]
10. (c)(i)The student finds that when CH3CHCICOOH and NH3 are added in a 1:1 stoichiometric ratio, the conjugate acid and base of the reactants are quickly formed. reaction 1 CH3CHCICOOH + NH3 → CH3CHCICOO⁻ + NH4⁺ Identify the conjugate acid-base pairs in reaction 1.[1]
11. (c)(ii)A student investigates the rate of reaction 2. The student mixes CH3CHCICOO⁻ with a large excess of NH3. The graph in Fig. 5.3 shows the results obtained. [Figure 5.3] Use the graph in Fig. 5.3 to show that reaction 2 is first order with respect to [CH3CHCICOO⁻].[2]
12. (c)(iii)Explain why a large excess of NH3 needs to be used in order to obtain the results in Fig. 5.3.[1]
13. (c)(iv)The student measures the effect of changing the concentration of NH3 on the rate of reaction 2. Table 5.1 shows the results obtained. Table 5.1 experiment [CH3CHCICOO⁻] /mol dm⁻³ [NH3] /mol dm⁻³ initial rate of reaction /mol dm⁻³s⁻¹ 1 0.00120 0.00300 1.47 x 10⁻⁵ 2 0.00120 0.00450 2.21 x 10⁻⁵ Use the information in Table 5.1 and in (c)(ii) to determine whether the nucleophilic substitution reaction proceeds via an SN1 or an SN2 mechanism. Explain your answer.[2]
14. (c)(v)Describe the effect of an increase in temperature on the rate of reaction of CH3CHCICOO⁻ and NH3. Explain your answer.[2]
15. (c)(vi)When an excess of CH3CHCICOO⁻ is used, further substitution reactions occur. One product has the formula C6H9NO4²⁻. Suggest the structure of C6H9NO4²⁻.[1]

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